Redundant communication path for satellite communication data

ABSTRACT

According to one embodiment, a method for use in managing satellite communications includes: receiving, at a first earth-based gateway antenna system, one or more microwave communication signals from a substantially geostationary satellite; monitoring for a performance change in at least one signal from the satellite; and, in response to detecting a performance change in the at least one signal, transmitting instructions to the satellite to transmit at least a portion of the one or more microwave communication signals to a second earth-based gateway antenna system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 11/847,102, filed Aug. 29, 2007, which application claims thebenefit of U.S. Provisional Application Ser. No. 60/840,809, filed Aug.29, 2006. These applications are specifically incorporated herein, byreference, for all that they disclose and teach.

TECHNICAL FIELD

This invention relates generally to communication systems, and moreparticularly to a network-access satellite communication system.

BACKGROUND

Commercial satellites have historically been optimized for broadcastapplications, where data are transmitted from a broadcast center on theearth up to a satellite in space, and the satellite retransmits thesesignals down to a population of receive-only earth stations or satelliteterminals on the earth. Traditional broadcast satellites arecharacterized by two features. First, traditional broadcast satellitesprovide “one-way” communications, such that the recipient of the data(i.e. the end-user) is equipped with a receive-only terminal that has noability to transmit a signal back up to the satellite. Second,traditional broadcast satellites are designed for wide geographiccoverage using antennas or combinations of antennas on the satellitewith beams that cover large regional, national, or continental areas.

A typical business goal for traditional broadcast satellite operators isto provide as much data as possible (e.g., hundreds of televisionchannels) to a large number of end-users or customers. For content ofnational or international interest (e.g., televised sports, movies andnews), a satellite operator may choose to broadcast the same data to anentire country or even to an entire continent. A video broadcastsatellite, with a single antenna beam covering the continental U.S. andproviding hundreds of television channels to U.S. customers, is a goodexample of a traditional broadcast satellite. For regional content, somebroadcast satellites have several antenna beams that effectively dividethe earth terminal population into large regional groups such thatcertain combinations of the broadcast data content are transmitted toeach group. In both cases, the broadcast satellite system providesone-way communications to customers over a large geographic area.

Using a traditional broadcast satellite with antenna beams coveringentire national or large regional areas to private communications with asingle terminal somewhere in the coverage area is not an efficientapproach for network-access satellite services. For example, if acustomer with a two-way earth terminal located in New York wants toestablish a private two-way connection to the Internet, transmittingenergy from a satellite over the entire continental U.S. to sendinformation to a single customer in New York would be an inefficient useof limited and costly satellite resources.

In recent years, satellite operators have used satellites to providenetwork-access services (e.g., telephony, private networks, and Internetaccess) to a large population of end-users or customers. In modernnetwork-access satellite communications systems, end-users are equippedwith earth terminals that both receive signals from a satellite and alsotransmit signals back up to a satellite. Modern network-access satellitesystems are architecturally different from traditional one-way broadcastsatellite systems in that each earth terminal is, in effect, carrying ona two-way private conversation with the satellite network and generallyhas no interest in “hearing” signals being transmitted to and from anyother earth terminals on the network.

A satellite with a more highly focused antenna beam limited in area toan individual customer's immediate local area s a much more efficientway for transmitting data to this particular customer than a traditionalbroadcast satellite. Similarly, in the earth-to-space direction, if areceiver on a satellite is focused in on a much narrower geographicalregion that covers just the customer's immediate area, less power isrequired for that customer's earth terminal to transmit information tothe highly focused receiver on the satellite.

Modern network-access satellites are characterized by two features.First, modern network-access satellites provide “two-way” communicationsbetween satellites in space and terminals on the earth that have bothtransmit and receive capability. Second, modern network-accesssatellites are designed with antennas that cover the geographic area ofinterest on the earth with many smaller antenna beams, often tightlypacked together to provide full coverage across the area of interestwithout any gaps. For example, some modern network-access satellitestransmit tightly packed clusters of small antenna beams thatcollectively cover a large geographic area, such as the continental U.S.For two-way network-access communications, by using a number of“spot-beams” over their coverage area, spot-beam satellites havesignificant advantages over satellites that have a single beam over thecoverage area. For example, spot-beam satellites require less satellitetransmitter power per customer. As another example, less transmitterpower is required for earth terminals to transmit to spot-beamsatellites, allowing for smaller and less expensive earth terminals.Additional advantages include the ability to reuse the same frequencybands and channels throughout the spot-beam pattern and associatedcoverage area, dramatically higher non-broadcast capacity per satelliteto provide more compelling services to more customers, and dramaticallylower satellite cost per customer. For example, the capacity of aspot-beam satellite to support a large population of end-users may begreatly enhanced by frequency reuse techniques, whereby the samefrequency bands and channels are used over and over again innon-adjacent spot-beams. For example, a satellite operator may have a500 MHz bandwidth allocation for space to earth transmissions assignedby the appropriate regulatory authority. In a single beam networkarchitecture, this satellite operator is limited to 500 MHz of totaltransmission bandwidth. The transmission bandwidth may be increased bydividing this bandwidth into multiple channels, such as for example,four 125 MHz channels, and assigning one channel to each of numerousspot-beams. In this example, if the satellite utilizes 100 spot-beams,this satellite operator could utilize 12,500 MHz of total transmissionbandwidth. This ability to apply frequency reuse techniques to greatlyincrease the capacity of a satellite network is a technical advantage ofthe spot-beam satellite architecture.

Overview

Particular embodiments of the present invention may reduce or eliminateproblems and disadvantages associated with previous network-accesssatellite communications systems.

According to one embodiment, a satellite communications system includesfirst, second, and third microwave radiators; first and second signalsplitters; and a selector. The first microwave radiator is configured todirect microwave signals to a first earth-based gateway antenna system,the microwave signals carrying communications data from a first userterminal located in a spot beam coverage region; and the first signalsplitter is configured to collect at least a portion of communicationsdata from the first user terminal. The second microwave radiator isconfigured to direct microwave signals to a second earth-based gatewayantenna system, the microwave signals carrying communications data froma second user terminal; and the second splitter is configured to collectat least a portion of communications data from the second user terminal.The third microwave radiator is configured to direct microwave signalsto a third earth-based gateway antenna system; and the first selector isconfigured to selectively couple the third microwave radiator to aselected one of the first and second splitters, such that the microwavesignals directed by the third microwave radiator carry communicationsdata collected from the selected one of the first and second splitters.

According to another embodiment, a satellite communications systemincludes first, second, and third feed horns; first and seconddirectional couplers; and a switch. The first feed horn is configured todirect microwave signals to a first earth-based gateway antenna system,the microwave signals carrying communications data from a first userterminal located in a spot beam coverage region; and the firstdirectional coupler is configured to collect at least a portion ofcommunications data from the first user terminal. The second feed hornis configured to direct microwave signals to a second earth-basedgateway antenna system, the microwave signals carrying communicationsdata from a second user terminal; and the second directional coupler isconfigured to collect at least a portion of communications data from thesecond user terminal. The third feed horn is configured to directmicrowave signals to a third earth-based gateway antenna system; and thefirst switch is configured to selectively couple the third feed horn toa selected one of the first and second directional couplers, such thatthe microwave signals directed by the third feed horn carrycommunications data collected from the selected one of the first andsecond directional couplers.

According to another embodiment, a method of mitigating microwave signalpropagation loss for satellite communications includes: transmitting afirst microwave signal from a satellite to a first earth-based gatewayantenna system, using a first microwave radiator, the microwave signalscarrying communications data from an earth-based user terminal;detecting propagation loss in at least one signal between the satelliteand the first earth-based gateway antenna system; and transmitting asecond microwave signal from the satellite to a second earth-basedgateway antenna, using a second microwave radiator, the second microwavesignal carrying communications data from the earth-based user terminal.

According to another embodiment, a method for use in managing satellitecommunications, comprising: receiving, at a first earth-based gatewayantenna system, one or more microwave communication signals from asubstantially geostationary satellite; monitoring for a performancechange in at least one signal from the satellite; and in response todetecting a performance change in the at least one signal, transmittinginstructions to the satellite to transmit at least a portion of the oneor more microwave communication signals to a second earth-based gatewayantenna system.

According to another embodiment, a method for use in managing satellitecommunication signal traffic, comprising: monitoring, at a satellite, asignal from a first earth-based gateway antenna system; and in responseto detecting a performance change in the monitored signal, transmittingone or more microwave communication signals from the satellite to asecond earth-based gateway antenna system.

In certain embodiments, an additional gateway may be utilized to provideone or more benefits to a satellite communications system. For example,an additional gateway may be used to provide improved performance bytransferring capacity from an existing gateway to the additional gatewayin periods when the existing gateway is experiencing problems due to,for example rain or weather fade. As another example, an additionalgateway may be used as a backup gateway in cases of a failure at anexisting gateway. Certain embodiments may provide all, some, or none ofthe advantages discussed above. In addition, certain embodiments mayprovide one or more other advantages, one or more of which may bereadily apparent to those skilled in the art from the figures,descriptions, and claims included herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and certainof its advantages, reference is now made to the following description,taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an example network-access satellite communicationsystem;

FIG. 2 illustrates example coverage regions for a spot-beamnetwork-access satellite communications system;

FIG. 3 illustrates an example payload for a spot-beam network-accesssatellite;’

FIG. 4 illustrates an example downstream signal path through examplecomponents of a network-access satellite;

FIG. 5 illustrates an example upstream signal path through examplecomponents of a network-access satellite;

FIGS. 6A and 6B illustrate example upstream and downstream signal pathsthrough example components of a network-access satellite;

FIGS. 7 and 8 illustrate example components that may be used to provideincremental capacity for a network-access satellite;

FIG. 9 illustrates example components that may be used to implementnon-contiguous beams;

FIGS. 10A through 10C illustrate example components that may be used toimplement a utility gateway;

FIG. 11 illustrates example components that may be used to controlsignal power;

FIG. 12 illustrates an example method for use in controlling signalpower;

FIG. 13 illustrates example components that may be used to controlsignal power;

FIG. 14 illustrates an example method for use in controlling signalpower; and

FIGS. 15A through 15C illustrate example signals associated with anexample method for use in controlling signal power.

DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 illustrates an example network-access satellite communicationssystem 100. System 100 includes satellite 10, one or more gateways 20,and one or more user terminals 32. In operation, system 100 provides fortwo-way communications between user terminals 32 and network 70 throughsatellite 10 and gateway 20. Satellite 10 includes payload 80 and one ormore solar arrays 90. In certain embodiments, satellite 10 may be ageosynchronous or geostationary satellite although in alternativeembodiments any appropriate orbit for satellite 10 may be used.Satellite 10 represents a spot-beam network-access satellite configuredto communicate with a population of user terminals 32 distributed acrossa defined coverage area. Each user terminal 32 in communication withsatellite 10 is positioned within at least one spot beam coverage region30. User terminals 32 are two-way capable and may be designed withadequate transmit power and receive sensitivity to communicate reliablywith satellite 10. Satellite 10 communicates with user terminals 32 bysending and receiving signals through one or more spot beams 40.

Satellite 10 communicates with gateway 20 through signals traveling inbeam 60. Gateway 20 sends and receives signals to and from satellite 10using gateway antenna system 22 located within gateway region 50.Gateway 20 is connected to one or more networks 70. Network 70 mayrepresent a local area network (LAN), metropolitan area network (MAN),wide area network (WAN), global communications network such as theInternet, a telephony network, such as the Public Switched TelephoneNetwork (PSTN), or any other suitable public or private network.

FIG. 2 illustrates example spot beam coverage regions 30 for spot-beamnetwork-access satellite communications system 100. In the embodimentshown, a pattern of spot beam coverage regions 30 is used to providecoverage for an example satellite coverage area 34. Satellite coveragearea 34 may include land masses, water or ocean areas, or a combinationof land masses and water areas. As shown in FIG. 2, satellite coveragearea 34 represents the continental United States and portions of Alaska.Although any appropriate pattern may be used for spot beam coverageregions 30, in certain embodiments, spot beam coverage regions 30 may bedistributed in a pattern that provides continuous coverage throughoutsatellite coverage area 34. In certain embodiments, one or more spotbeam coverage regions 30 may overlap at least in part with one or moreother spot beam coverage regions 30.

In certain embodiments, network access may be provided to the spot beamcoverage regions 30 within satellite coverage area 34 using one or moresatellites 10. In addition, each satellite 10 providing network accessto satellite coverage area 34 may receive signals from one or moregateways 20. In certain embodiments, each satellite 10 may receivesignals from as many as ten or more gateways 20 to provide networkaccess to user terminals 32 within multiple spot beam coverage regions30 in satellite coverage area 34.

FIG. 3 illustrates an example payload 80 for satellite 10. Payload 80includes antenna reflectors 82, feed horn clusters 84, telemetry commandand ranging (TC&R) horn 88, and beacon horn 89. Each feed horn cluster84 may include numerous feed horns 86. In operation, microwave signalsmay be transmitted by one or more feed horns 86 and then focused onto aparticular region of the earth by antenna reflector 82. In certainembodiments, antenna reflector 82 may represent a Ka band transmitreflector, a Ka band receive reflector, or any appropriate reflector fordirecting the transmission path of microwave signals in the appropriatefrequency band. In certain embodiments, particular antenna reflectors 82and feed horn clusters 84 may be utilized to transmit signals fromsatellite 10, while particular antenna reflectors 82 and feed hornclusters 84 may be utilized to receive microwave signals at satellite10. In alternative embodiments, satellite 10 may utilize one or more oftwo-way antennas, direct radiating antennas, array antennas, or otherelectromagnetic transducers.

In operation, through the use of multiple feed horns 86 within a feedhorn cluster 84, a plurality of spot beams 40 may be projected intosatellite coverage area 34, such that each spot beam 40 defines aparticular spot beam coverage region 30. Similarly, each particular feedhorn 86 within a feed horn cluster 84 may operate together with antennareflector 82 to receive microwave signals within a particular spot beam40 from one or more user terminals 32 within a particular spot beamcoverage region 30. In certain embodiments, one or more dedicated feedhorns 86 may be used to transmit microwave signals through one or morebeams 60 to one or more gateways 20 within gateway region 50. Inalternative embodiments, when a gateway 20 is located within aparticular spot beam coverage region 30, satellite payload 80 may beconfigured such that a particular feed horn 86 transmits (or receives)microwave signals to (or from) one or more user terminals 32 and gateway20. In certain embodiments, a gateway region 50 may be included withinor overlap with one or more spot beam coverage regions 30. In certainembodiments, a gateway region 50 may be entirely outside satellitecoverage area 34.

Although feed horns are illustrated in the drawings and identifiedthroughout this description, in certain embodiments other suitablemicrowave radiators can be used together or as an alternative to feedhorns. For example, and not by way of limitation, other suitablemicrowave radiators may include phased arrays, direct radiatingapertures, slotted arrays, and helical radiators. Various embodimentsmay be utilized any suitable microwave radiator without departing fromthe scope of the invention.

The operation of system 100 can be separated into a forward (downstream)direction and a return (upstream) direction. In the downstreamdirection, data arrives at gateway 20 from network 70, gateway 20transmits that data up to satellite 10, and satellite 10 relays thatdata down in a spot beam 40 to user terminal 32 in region 30. In theupstream direction, user terminal 32 transmits data up to satellite 10,satellite 10 relays that data down to gateway 20, and gateway 20forwards that data to network 70.

Although the components of satellite payload 80 are described herein andillustrated in FIGS. 4-10A and 13 as analog components that may be usedto guide and manipulate microwave signals, in alternative embodiments,one or more digital components may be used in addition to or as analternative to the use of analog components. For example, satellitepayload 80 may include one or more analog-to-digital converters, digitalsignal processors, and/or digital-to-analog converters. In variousembodiments, one or more of the functions described herein may beperformed with analog components, digital components, or a combinationthereof without departing from the scope of the invention.

FIG. 4 illustrates an example downstream signal path through examplecomponents of satellite payload 80. For example, In the embodimentshown, a microwave signal may be received from gateway antenna system22, split into multiple channels, amplified, and transmitted througheight different spot beams 40 to eight different spot beam coverageregions 30. Although the example components may be utilized to transmitsignals through eight different spot beams 40, in alternativeembodiments, more or fewer components may be utilized to provide more orfewer functions than those described below, and may be utilized totransmit signals through more or fewer spot beams 40.

Moving from left to right in FIG. 4, microwave signals are received fromgateway 20 through beam 60 at feed horn 86. The signals travel throughpolarizer 102 and switch 104 into low noise amplifier 106. As with manyof the components described herein, within satellite payload 80 many ofthe components may be implemented with redundancies designed to increasethe longevity of satellite 10 in the event of failure of one or morecomponents. This redundancy may be implemented through the use ofmultiple components distributed in parallel or in a ring configuration.Although particular configurations are shown and described herein ashaving specified numbers and configurations of redundant components, inalternative embodiments, any appropriate number and configuration ofcomponents may be utilized to achieve the desired level of redundancy.Accordingly, as shown in FIG. 4 there are two low noise amplifiers 106distributed in parallel along the signal path. The signal traveling outof low noise amplifier 106 travels through another switch 104 and intodown converter 108. Again, in the embodiment shown down converter 108 isdoubly redundant with two down converters 108 implemented in parallelalong the signal path. From down converter 108, the signal travelsthrough a third switch 104 and into input multiplexer 110. In theembodiment shown, input multiplexer 110 is a one-to-four multiplexerwith one signal input and four signal outputs. The four signal outputsshown on the right side of input multiplexer 110 represent fourdifferent channels from the input signal on the left-hand side of inputmultiplexer 110. In this example embodiment, these four output channelstravel from input multiplexer 110 into a bank of ring redundancyswitches 112. In the embodiment shown, ring redundancy switches 112provide for six potential signal paths for these four signal channels.The signal channels traveling from ring redundancy switches 112 travelthrough a channel amplifier 114 and into traveling wave tube (TWT)amplifier 116 before returning to a second bank of ring redundancyswitches 112. From the second bank of ring redundancy switches 112, eachsignal channel travels to an output multiplexer 118 which divides eachof these four signal channels into two separate channels for a total ofeight signal channels. Each of these eight signal channels is thenpolarized using polarizer 102 and transmitted using feed horn 86 througha spot beam 40 to one or more user terminals 32 within particular spotbeam coverage regions 30. In various embodiments, polarizers 102 may beimplemented for use with multi-band or dual-band signals utilizinglinear (vertical/horizontal) polarization and/or circular(left-hand/right-hand) polarization. In alternative embodiments, more orfewer components may be utilized to provide the same, more, or fewerfunctions.

FIG. 5 illustrates an example upstream signal path through examplecomponents of satellite payload 80. In the embodiment shown, microwavesignals may be received from user terminals 32 located within eightdifferent spot beam coverage regions 30 amplified, combined into asingle composite signal, and transmitted through a spot-beam 60 togateway antenna system 22. Although the example components may beutilized to receive signals from user terminals 32 located in eightdifferent coverage areas 30, in alternative embodiments, more or fewercomponents may be utilized to provide more or fewer functions than thosedescribed below, and may be utilized to receive signals from userterminals 32 located in more or fewer spot beam coverage regions 30.

Moving from right to left in FIG. 5, upstream communication signals arereceived from one or more user terminals 32 through spot beam 40 at feedhorn 86. The communication signals then pass through polarizer 102 andswitch 104 into low noise amplifier 106. As shown in FIG. 5, low noiseamplifier 106 is shown as two-for-one redundant with two low noiseamplifiers 106 distributed in parallel along the signal path. From lownoise amplifier 106, the signal passes through switch 104 and into inputmultiplexer 120. In the embodiment shown, the upstream signals fromeight different feed horns feed into input multiplexer 120 whichcombines these eight signals into a single composite signal. From inputmultiplexer 120, the composite signal travels through switch 104 andinto down converter 122. In the embodiment shown, two for one sparing isutilized with two down converters 122 distributed in parallel along thesignal path. From down converter 122, the composite signal travelsthrough switch 104, into. As with down converter 122, in the embodimentshown, two for one sparing is utilized for channel amplifier 114 andtraveling wave tube amplifier 116 with each of these componentsdistributed in parallel. From traveling wave tube amplifier 116, thecomposite signal travels through switch 104 and into transmission filter124. The composite signal is then polarized using polarizer 102 andtransmitted by feed horn 86 through beam 60 to gateway 20. Inalternative embodiments, more or fewer components may be utilized toprovide the same, more, or fewer functions

In the embodiments shown in FIGS. 4 and 5, communication signalstraveling to and from gateway 20 utilize a separate feed horn 86 fromthe feed horns 86 utilized for communications to and from user terminals32. However, in alternative embodiments, as discussed above, one or morefeed horns 86 may send and/or receive communication signals to gateway20 and one or more user terminals 32.

FIGS. 6A and 6B illustrate example upstream and downstream signal pathsthrough example components of satellite payload 80, in which one or morefeed horns 86 are utilized to communicate both with one or more gatewaytransmitters 22 and one or more user terminals 32.

Incremental Capacity

In embodiments of system 100 utilized to provide network access to apopulation of user terminals 32, numerous gateways 20 may be required.Each gateway 20 may be expensive to construct and may require costlymanpower to maintain and operate. Following initial launch, satellite 10may experience a light signal traffic load for a period of time untildemand increases. During this period of time, while satellite 10 isoperated below capacity, the number of gateways 20 required to providesufficient coverage may be less than the entire set of gateways 20required to support full capacity. Constructing and operating the entireset of gateways 20 during initial operations when the satellite isexperiencing a light signal traffic load may be prohibitively expensive.The ability to launch a new satellite and immediately provide fullgeographic coverage with a smaller number of gateways 20, and then addadditional gateways incrementally as required to support increasingdemand, has significant economic advantages. One way to provide suchincremental capacity is through a “filter-and-switch” approach. Afilter-and-switch approach allows the bandwidth (or channels) fromcertain gateways 20 to be divided into two or more subsets, where eachsubset is assigned to a group of feed horns 86 using switches withinpayload 80 of satellite 10.

FIG. 7 illustrates example components that may be included in payload 80to provide incremental satellite capacity in the downstream directionusing a filter-and-switch approach. In the example shown in FIG. 7, asingle gateway 20 may be used initially to provide network-access touser terminals 32 located in six spot beam coverage regions 30associated with six different spot beams 40. Using these components,incremental capacity may be added through the use of switches 202 andthe addition of an additional gateway 20. In this initial configuration,all of the switches 202 are set to position “1” to support six spot beamcoverage regions 30 with a single gateway 20. Moving from left to rightin FIG. 7, the communication signals are initially received at feed horn86 a from beam 60 a. In the single gateway configuration, the signalsreceived at feed horn 86 a pass through switch 202 a (set at position“1”) and into channel filters 204 a and 204 b. Communication signals forchannels 1 through 3 pass from channel filter 204 a through switch 202 b(set at position “1”) and into power combiners 212 a through 212 c.Using these components, the communication signals associated withchannel 1 are transmitted by feed horn 86 b to one or more userterminals 32 through spot beam 40 a. Similarly, the communicationsignals associated with channel 2 are transmitted by feed horn 86 c andthe communication signals associated with channel 3 are transmitted byfeed horn 86 d. The communication signals associated with channels 4through 6 leave channel filter 204 b, pass through switch 202 c (set atposition “1”), and arrive at power combiners 212 d through 212 f. Usingthese components the communication signals associated with channel 4 aretransmitted by feed horn 86 e to one or more user terminals 32 throughspot beam 40 d. Similarly, the signals associated with channel 5 aretransmitted by feed horn 86 f and the communication signals associatedwith channel 6 are transmitted by feed horn 86 g.

Using the filter-and-switch approach illustrated, the capacity ofsatellite 10 may be increased by adding an additional gateway 20 tosupport the six spot beam coverage regions 30. In this configuration,all of switches 202 are set to position “2,” such that feed horns 86 bthrough 86 d are supported by a first gateway 20 in communication withfeed horn 86 a and feed horns 86 e through 86 g are supported by asecond gateway 20 in communication with feed horn 86 h. In thisconfiguration, moving from left to right in FIG. 7, the communicationsignals received at feed horn 86 a pass through switch 202 a (set atposition “2”) and into channel filter 204 c. From channel filter 204 c,the communication signals travel through switch 202 b (set at position“2”), through power combiners 212 a through 212 c, and are thentransmitted by feed horns 86 b through 86 d. The communication signalsreceived by feed horn 86 h pass through channel filter 206, throughswitch 202 c (set at position “2”), through power combiners 212 dthrough 212 f, and are transmitted by feed horns 86 e through 86 g.

Using the example filter-and-switch approach illustrated, spot beams 40a through 40 f may be serviced at half capacity using a single gateway20, as shown in FIG. 7 with switches 202 set at position “1,” orserviced at full capacity using two gateways 20, as shown in FIG. 7 withswitches 202 set at position “2.” The filter-and-switch approach for usein the upstream direction may be implemented in a similar manner.

In alternative embodiments, incremented capacity may be provided withfewer filters and switches than used with the “filter-and-switch”approach. For example, such incremental capacity may be provided using a“direct-connect” approach. Using the direct-connect approach, gateways20 may be connected to spot beams 40 such that a first portion of eachspot beam 40 capacity may be serviced by a first gateway 20 and a secondportion of each spot beam 40 capacity may be serviced by a secondgateway 20. This approach can be extended and scaled to allow variousportions of the capacity of particular spot beams 40 to be serviced bymultiple gateways 20, such that the operational capacities of theseparticular spot beams 40 increase in increments as each additionalgateway 20 is built and activated.

FIG. 8 illustrates example components that may be included in satellitepayload 80 to provide incremental capacity in the downstream directionusing a direct-connect approach. In the example shown, a single gateway20 may be used to initially provide network access to user terminals 32located in six spot beam coverage regions 30 associated with sixdifferent feed horns 86. Using these components, incremental capacitymay be added without changing the configuration of the components insatellite payload 80. Moving from left to right in FIG. 8, thecommunication signals are initially received at feed horn 86 a throughbeam 60 a. The communication signals received at feed horn 86 a aredirected through channel filter 206 a. From channel filter 206 a, thecommunications signals are split and directed through six frequencyselective power combiners. In the embodiment shown, the communicationssignals are split into six different wave paths; however, in alternativeembodiments, other variations may be used with an alternative number ofwave paths and/or power combiners.

As shown in FIG. 8, the communication signals received by feed horn 86 aare filtered by channel filter 206 a, split, directed through sixdifferent frequency selective power combiners 212 a through 212 f andtransmitted by feed horns 86 b through 86 g. The communication signalsreceived by feed horn 86 h are directed to channel filter 206 b. Fromchannel filter 206 b, the communications signals are split six waysthrough the use of a microwave signal splitter or other appropriatedevice. In the embodiment shown, the communications signals are splitinto six different wave paths; however, in alternative embodiments,other variations may be used with an alternative number of wave paths.In addition, although the number of wave paths used for thecommunications signals received by feed horn 86 a is the same as thenumber of channels utilized for the communications signals received byfeed horn 86 h, in alternative embodiments, these numbers may vary fromeach other, such that the one-to-one ratio is not maintained. Eachchannel of communication signals is then directed through a frequencyselective power combiner in communication with a feed horn 86. Inalternative embodiments, rather than utilize a signal splitter and afrequency selective power combiner, a multiplexer and a power combinermay be used.

In embodiments in which a single gateway 20 is transmittingcommunication signals through beam 60 a to feed horn 86 a, spot beams 40a through 40 f may be serviced at half capacity. In embodiments in whichtwo gateways 20 are transmitting communication signals and thesecommunication signals are received at feed horns 86 a and 86 h throughbeams 60 a and 60 b, power combiners 212 combine selected channels ofcommunication signals received from both feed horns 86 a and 86 h. Asshown in FIG. 8, in certain embodiments, the channels selected to becombined in each of power combiners 212 a through 212 f may be selectedsuch that each power combiner frequency selects two distinct channels toavoid interference. By combining the communication signals from beams 60a and 60 b, spot beams 40 a through 40 f may be serviced at fullcapacity. The direct-connect approach for use in the upstream directionmay be implemented in a similar manner.

The direct-connect approach, may provide a lower cost and increasedreliability solution for a network-access satellite with incrementalcapacity. For example, the direct-connect approach may be less expensivethan the filter-and-switch approach because the direct-connect approachdoes not require the added weight and cost of additional filters andswitches. As another example, the direct-connect approach may be morereliable because it utilizes fewer switches and filters in the primarysignal path than the filter-and-switch approach. In certain embodiments,the provision of incremental capacity may allow each spot beam 40 to beserviced by multiple gateways, such that only a portion of the capacityis lost if a gateway 20 suffers an outage. Certain embodiments mayeasily be scaled to any number of gateways 20 and any number ofassociated spot beams 40. In certain embodiments, satellite payload 80may be configured such that certain spot beams 40 have one associatedgateway 20, certain spot beams 40 have two associated gateways 20,certain spot beams 40 have three associated gateways 20, etc.

Non-Contiguous Beams

Demand for network-access satellite services may be non-uniform withinsatellite coverage area 34. In certain embodiments, network-accesssatellite communication system 100 may be configured to providenon-uniform capacity within satellite coverage area 34. For example,system 100 may be configured to provide (1) larger spot beams 40 tocover lower density spot beam coverage regions 30; (2) lower bandwidthfor spot beams 40 covering lower density spot beam coverage regions 30;(3) lower power transmitters to serve spot beams 40 covering lowerdensity spot beam coverage regions 30; and (4) non-contiguous spot beams40. Non-contiguous beams may provide both non-uniform capacity andflexibility to balance capacity across two or more beams withoutphysical switching or processing on satellite 10. An examplenon-contiguous beam may be implemented as two or more downstream spotbeams 40 that may transmit identical, or substantially identical,communication signals over the same channel to multiple non-contiguousspot beam coverage regions 30 and as two or more upstream spot beams 40that may be received and processed by payload 80 as a single spot beam40 or as a single channel.

Transmitters 32 throughout the non-contiguous spot beam coverage regions30 may share the same increment of satellite capacity. In particular,satellite 10 may transmit the same downstream signal to all transmitters32 in multiple non-contiguous spot beam coverage regions 30 and mayprocess upstream signals from transmitters 32 in multiple non-contiguousspot beam coverage regions 30 as if they were located in a single spotbeam coverage region 30. In certain embodiments, the downstream signalmay be power divided into two or more signals, which may occupy the samebandwidth and may have equal or unbalanced power. These signals may thenbe transmitted using two or more feed horns 86 to two or morenon-contiguous and non-overlapping spot beam coverage regions 30. In theupstream direction, receive signals from two or more feed horns 86 maybe power combined and processed as a single signal. This approach may bescaled to any number of spot beam coverage regions 30.

In certain embodiments, capacity may be efficiently shared acrossmultiple spot beam coverage regions 30 using, for example, time domaintechniques such as time division multiple access (TDMA) technology. In asatellite network where each user terminal 32 performs turn-aroundranging, either to the satellite or through the satellite, to establisha time delay reference, user terminals 32 in each spot beam coverageregion 30 supported by a single communication channel may share capacityon a single TDMA waveform.

In certain embodiments, the use of non-contiguous spot beams 40 mayallow shared capacity across multiple spot beam coverage regions 30supported by a single communication channel. In certain embodiments, theuse of non-contiguous spot beams 40 may allow spot beam coverage regions30 to be the same size and shape as other spot beam coverage regions 30in a uniform pattern within satellite coverage area 34, which mayprovide improved performance and may minimize interference in a tightlypacked pattern of spot beam coverage regions 30. In certain embodiments,the use of non-contiguous spot beams 40 may provide for the shared useof the identical, or substantially identical, signals, (including burstrates, bandwidths, and waveforms) in beam areas where the demand fornetwork access may be dramatically lower than the average beam capacity.

FIG. 9 illustrates example components that may be included in payload 80to implement non-contiguous spot beams 40, according to particularembodiments. The components illustrated in FIG. 9 may be used incombination with and/or as an alternative to one or more of thecomponents illustrated in FIG. 4, 5, or 6A-6B. In the embodiment shown,signals generated by transmitter 230 are passed to power divider 232which then passes the signals on to both transceiver 234 a andtransceiver 234 b. As used herein, a transceiver is a device configuredto allow upstream and downstream signals to be transmitted and/orreceived through the same node, device, and/or path. In certainembodiments, a transceiver may or may not include or be coupled to adiplexer, a transmit-receive filter, or other similar device.

Signals from transceiver 234 a are then transmitted by feed horn 236 athrough spot beam 40 a to spot beam coverage region 30 a. Similarly,signals from transceiver 234 b are transmitted by feed horn 236 bthrough spot beam 40 b to spot beam coverage region 30 b. Through theuse of these components, a single signal generated by transmitter 230 amay be distributed to two non-contiguous spot beam coverage regions 30 aand 30 b. Similarly, signals generated by one or more transmitterswithin spot beam coverage region 30 a may be transmitted through spotbeam 40 a and received by feed horn 236 a. These signals may then bedirected through transceiver 234 a and into power combiner 238. At thesame time, signals generated by one or more transmitters 32 within spotbeam coverage region 30 b may be transmitted through spot beam 40 b andreceived by feed horn 236 b. These signals may be directed throughtransceiver 234 b and into power combiner 238. The signals generated bytransmitter 32 within spot beam coverage regions 30 a and 30 b may becombined within power combiner 238 and directed to receiver 239. Incertain embodiments, techniques such as time-division multiplexing,frequency-division multiplexing, and code-division multiplexing may beused to combine communications signals associated with non-contiguousregions using a single channel or discrete frequency band.

Mitigating Rain Fade

Certain types of weather, especially the heavy rain often associatedwith thunderstorms, can cause significant propagation loss orattenuation of electromagnetic waves, particularly at microwave andmillimeter wave frequencies. In a network-access satellite system, manytens of thousands of user terminals 32 may access network 70 through asingle gateway 20. Disruptive weather between a particular gateway 20and satellite 10 could result in disruption of service for all userterminals 32 who connect to network 70 through that particular gateway20.

One approach to mitigating propagation loss or attenuation due todisruptive weather such as heavy rain (i.e., “rain fade” or “weatherfade”) is to build a second, backup gateway 20, which may be near thefirst gateway 20 but far enough away from the primary gateway 20 suchthat the probability of both gateways 20 being simultaneously affectedby weather is diminishingly small. Using this approach, a second gateway20 may be built for every primary gateway 20 that transmits signals tosatellite 10. Using this approach, each second gateway 20 would notprovide any additional capacity or generate any additional revenue.Another approach to mitigating weather fade is to build a utilitygateway 250 with utility transceiver 252.

This approach utilizes satellite 10 with a net capacity that utilizes anumber of operational gateways 20, for example N, and also utilizes autility gateway, for a total of N+1 gateways. The utility gateway cantake over the functions of any one of the N operational gateways. Thesatellite is designed with commandable switching, either automatic or byground control, to switch capacity from a gateway 20 sufferingpropagation loss or attenuation and at risk of outage to the utilitygateway. A single utility gateway may provide a weather diversity sitecapable of backing up any of the operational gateways 20 on a “one at atime” basis. In certain embodiments, network-access satellitecommunications system 100 may utilize more than one utility gateway.

FIG. 10A illustrates example components that may be used to implement autility gateway for use in mitigating weather fade and/or disaster at anoperational gateway. In the embodiment shown, the components areutilized to implement two operational gateways 20 a and 20 b and asingle utility gateway 250. In alternative embodiments, any number ofoperational gateways and utility gateways may be implemented usingsimilar components. FIG. 10A is intended to illustrate only thosecomponents which may be included in payload 80 to implement the utilitygateway function, according to certain embodiments. In variousembodiments, the components illustrated in FIG. 10A may be used togetherwith some or all of the components illustrated in FIG. 4, 5, or 6A-6B.

In the embodiment shown in FIG. 10A, for each operational gateway 22,payload 80 includes a transmitter 232, a transceiver 234, a feed horn236, and a receiver 238. These components may be utilized together withother components in payload 80 to transmit and/or receive communicationsignals to and/or from gateway 22 through beam 60. In certainembodiments, a utility gateway may be implemented by the addition ofdirectional couplers 240, switches 202, transmitter 242, transceiver244, feed horn 246, and receiver 248. For example, in the event of rainfade experienced at gateway 20 a, switches 202 may be set to position“1.” Utility gateway 250 may then be used to transmit and/or receivecommunication signals previously associated with operational gateway 20a. Similarly, in the event of rain fade experienced at operationalgateway 20 b, switches 202 may be set to position “2.” Utility gateway250 may then be utilized to transmit and/or receive signals previouslyassociated with operational gateway 20 b. In certain embodiments,switches 202 may have additional positions, such as an off position.Although directional couplers are discussed herein as an examplecomponent that may be utilized to combine or split a signal, anyappropriate active or passive combiner or splitter may be used toperform the functions provided by a directional coupler. In certainembodiments, as an alternative to or in addition to directional couplers240 or other appropriate active or passive combiner or splitter, one ormore switches may be utilized to direct communication signals to and/orfrom utility gateway 250.

An example of the utility gateway concept is shown in FIG. 10A for thecase where the functions of any one of two operational gateways 20 maybe replaced by a utility gateway 250. In certain embodiments, thetransition of communications traffic from an operational gateway 20 toutility gateway 250 may be performed all at once. As an alternative, thetransition of communications traffic may be performed incrementally. Forexample, the transition of communication traffic may be performedincrementally by channel or by other category.

In certain embodiments, the use of utility gateway 250 may substantiallymitigate the risk of service disruptions at multiple operationalgateways 20 by serving as a backup for multiple operational gateways 20on a one-at-a-time basis. In addition, the use of utility gateway 250,that can serve as a backup for multiple operational gateways 20, may beless expensive than building backup gateways for each operationalgateway 20 on a one-to-one basis. In particular embodiments, utilitygateway 250 may be located far enough from any operational gateway 20that the likelihood of a single storm affecting both an operationalgateway 20 and a utility gateway 250 is nearly zero. In certainembodiments, a utility gateway 250 may be located in a dry area, such asin a desert, or on a mountain top where the likelihood of a disruptiverain event at utility gateway 250 is diminishingly small.

A number of extensions of the utility gateway for weather relatedoutages can be envisioned, including (1) extending the concept to two ormore utility gateways 250 to provide protection from simultaneousdisruptive events at operational gateways 20; and (2) utilizing anoperational gateway 20 with adequate available capacity as a partialutility gateway to take over at least a portion of the functions ofanother operational gateway suffering disruption or weather propagationloss or attenuation.

Disaster Recovery

Gateways may be vulnerable to electrical failures, fire, flood, tornado,physical destruction, sabotage, or other risks that could result in thegateway being non-operational for an extended period of time. Methods tomitigate these risks may include any combination of careful sitelocation, facility hardening, and construction of backup gateways.Alternative methods may include the utilization of a transportablegateway which can be brought to or near the damaged gateway to quicklyprovide temporary service until the damaged gateway can be repaired. Asyet another alternative, a utility gateway may be utilized to mitigatethe risk of a disaster at an operational gateway. By utilizing a utilitygateway, a satellite operator may transfer all or a portion of the loadfrom a failed, damaged or otherwise non-operational gateway to a utilitygateway to quickly restore service. A satellite may utilize multipleutility gateways to provide simultaneous protection against multipleevents including weather and disaster related outages.

Network Management

In certain embodiments, a utility gateway 250 may be utilized tomonitor, on a non-interference basis, the signals from one or moreselected operational gateways 20 to satellite 10 and/or signals fromsatellite 10 to those selected operational gateways 20. A utilitygateway 250 with monitoring capabilities may be utilized to facilitatenetwork management by evaluating power levels, signal quality, loadinglevels, interference, and other key parameters associated with theselected operational gateways 20. Utility gateway 250 may utilize asingle instance of monitoring equipment to monitor an operationalgateway's full downstream and upstream communications traffic withoutusing any of the operational gateway's bandwidth or reducing itscapacity.

In order to monitor an operational gateway 20, the downstreamcommunications traffic from the operational gateway 20 to satellite 10is transmitted by satellite 10 to user terminals 32, and a copy of thedownstream traffic is also transmitted by satellite 10 to the utilitygateway 250. In a similar manner, satellite 10 may transmit a copy ofthe upstream communications traffic that is transmitted from satellite10 to the operational gateway 20 to utility gateway 250 for monitoring.

FIG. 10B illustrates example components that may be used to implement autility gateway 250 for use in network management. FIG. 10B is intendedto illustrate only those components which may be included in payload 80to implement a utility gateway 250 for use in network management,according to certain embodiments. In various embodiments, the componentsillustrated in FIG. 10B may be used together with some or all of thecomponents illustrated in FIG. 4, 5, or 6A through 6B. In the embodimentshown, the example components may be utilized to monitor upstream and/ordownstream traffic from one of operational gateways 20 a and 20 b,without disrupting the communication traffic to and/or from either ofoperational gateways 20 a and 20 b. Through the use of switches 202, aselection may be made as to which portion of communications traffic willbe monitored by utility gateway 250 at any given time. For example, inorder to monitor upstream network traffic at operational gateway 20 a,switch 202 a may be set to position “1” and switch 202 c may be set toposition “1,” as illustrated in FIG. 10B. As another example, downstreamcommunications traffic may be monitored at operational gateway 20 a bysetting switch 202 a to position “2” and setting switch 202 c toposition “1.” Communications traffic may be similarly monitored bysetting switch 202 c to position “2,” and setting switch 202 b to eitherposition “1” or “2” to monitor upstream or downstream traffic,respectively.

In certain embodiments, both the downstream and upstream communicationstraffic may be monitored simultaneously. In alternative embodiments,satellite 10 may be designed to monitor either upstream or downstreamcommunications traffic; the selection being either on a rotating basis,automatically selected by satellite 10, or in response to a command.Satellite 10 may also be designed to simultaneously monitor a portion,for example half, of the upstream traffic and a portion of thedownstream traffic; the particular portion being selected either on arotating basis, automatically selected by satellite 10, or in responseto a command.

Real-Time Performance Measurement

Some satellites utilize beams that transmit signals to a national orcontinental size region. For these satellites, a satellite operator maymonitor the performance of all of the signals being transmitted by thesatellite from a single site within these national or continentalregions. In contrast, a spot-beam satellite may have tens, hundreds, oreven more beams, with each beam directed to a smaller region. For thesespot-beam satellites, it may be difficult for a satellite operator toestablish, operate, and maintain monitoring facilities within each ofthese regions.

In certain embodiments, rather than monitoring downstream and upstreamcommunications traffic for an operational gateway 20 through the use ofmonitoring facilities located in many or all of these regions, a utilitygateway 250 may be utilized to monitor the corresponding downstream(satellite to end-user) and upstream (end-user to satellite)communication traffic associated with an operational gateway 20. In thismanner, a utility gateway 250 may be utilized to emulate end-users andperform two-way communications between these emulated end-users and theassociated operational gateway 20.

In certain embodiments, a number of end-users may be emulated at utilitygateway 250 for test and monitoring purposes. In certain embodiments,connectivity, speed, quality of service, and other performancemeasurements may be determined for the operational gateway 20 beingevaluated based on an evaluation of communications signals, testsignals, or simulated user terminal signals. In certain embodiments, asuite of end-user terminals may be emulated and connected, logically orby channel and band, into every beam, carrier, or group of actualend-users being serviced by the operational gateway 20. In this manner,the satellite operator may obtain real-time performance measurements asif the monitoring equipment were remotely located in each spot beamcoverage region 30. In certain embodiments, an ability to monitor thesignals in all, or substantially all, of spot beams 40 across an entirenetwork from a single site may greatly improve capabilities to managenetwork performance.

FIG. 10C illustrates example components that may be used to implement autility gateway 250 for use in performance measurement. FIG. 10C isintended to illustrate only those components which may be included inpayload 80 to implement a utility gateway 250 for use in performancemeasurement, according to certain embodiments. In various embodiments,the components illustrated in FIG. 10C may be used together with some orall of the components illustrated in FIG. 4, 5, or 6A through 6B. In theembodiment shown, the example components may be utilized to monitordownstream and upstream communication traffic associated with a selectedoperational gateway 20, without disrupting the communication traffic toand/or from the selected operational gateway 20. In the embodimentshown, the example components allow utility gateway 250 to selectivelymonitor communications traffic associated with either gateway 20 a orgateway 20 b. In alternative embodiments, components may be similarlyconfigured to allow a particular gateway 250 to selectively monitorcommunications traffic associated with a different number of operationalgateways 20. As shown in FIG. 10C, when switches 202 are set to position“1,” the communications signals transmitted by gateway 250 through beam60 c and received by feed horn 246 are received by receiver 248 andcoupled to the communications signal input to transmitter 232 fortransmission through feed horn 236 to operational gateway 20 a.Similarly, communications signals transmitted from gateway 20 a throughbeam 60 a are received by receiver 238 and directed to transmitter 242using directional coupler 240. From transmitter 242, the signals arefurther directed through beam 60 c to gateway 250. Through the use ofthese components, with switches 202 set to position “1,” gateway 250 mayemulate a user terminal 32 and measure the connectivity, speed, qualityof service, and other performance metrics over a complete communicationspath similar to the path utilized by an end-user at a user terminal 32.As shown in FIG. 10C, by setting switches 202 to position “2,” gateway250 may be utilized to emulate end-users associated with gateway 20 b.In certain embodiments, gateway 250 may be allowed to emulate end-usersassociated with various operational gateways 20 on a rotating basis,according to an automatically selected pattern, or in response to acommand.

Earth-Based Power Control Beacon

A beacon transmitter may be utilized on satellite 10 to transmit a knownsignal down to earth at a carefully controlled constant power level. Bymonitoring the beacon signal down on the earth, the signal path lossesbetween the satellite and the earth station of interest may bedetermined.

A satellite operator may monitor satellite beacon power to maintaintheir earth-to-space signals, such that the signals arrive at thesatellite at a constant power level. If the satellite beacon powerchanges, due to rain or other phenomena along the line of sight, thesatellite operator may adjust his earth station transmitter power by acorresponding amount to maintain a constant level at the satellite.Maintaining a constant signal power level at the satellite in thismanner may reduce interference and improve satellite performance.

Through the use of a satellite beacon a satellite operator may controlthe earth-based transmitters used to send signals up to satellite 10,but they provide little ability to control the transmitter power levelon board a satellite 10. On spot-beam satellite 10, the communicationslink from satellite 10 down to a gateway earth station 20 may consist ofhundreds or thousands of subscriber signals. By controlling the powerlevel of a satellite-to-gateway transmitter the performance of satellite10 may be improved.

In certain embodiments, the power level of a satellite-to-gatewaytransmitter may be controlled through the use of an earth-based beacontransmitter. This earth-to-space beacon signal may be received atsatellite 10 and transmitter power on satellite 10 may be dynamicallyand/or automatically adjusted based on the beacon signal power received.In certain embodiments, the use of dynamic and/or automatically adjustedtransmitter power may allow a transmitter to be operated at low power inlow-loss conditions and then operated at increased power levels onlywhen the loss along the propagation path increases. In certainembodiments, the use of dynamic and/or automatically adjustedtransmitter power may allow for (1) lower average power consumption onthe satellite; (2) less self-generated interference or distortion inlow-loss conditions; and (3) ability to rapidly increase satellitetransmitter power when the loss along the propagation path increases toreduce outages.

FIG. 11 illustrates example components that may be used to controltransmitter power level on board satellite 10. FIG. 11 is intended toillustrate only those components which may be included in payload 80 toimplement an earth-based power control beacon, according to certainembodiments. In various embodiments, the components illustrated in FIG.11 may be used together with some or all of the components illustratedin FIG. 4, 5, or 6A through 6B. In the embodiment shown in FIG. 11, anearth-based beacon signal may be received through feed horn 266 anddirected to beacon receiver 268. Beacon receiver 268 is coupled tocontroller 260 and information or signals from beacon receiver 268 maybe used as input to controller 260 which controls the power level fortransmitter 262. In this way, the earth-based beacon may be used tocontrol the signal power transmitted through beam 60 to gateway 20within gateway region 50. In the embodiment shown, feed horn 266 isfocused toward gateway region 50 to receive a beacon signal from anearth-based beacon located within gateway region 50. In this embodiment,both the earth-based beacon and gateway 20 would be co-located withinthe same gateway region 50. By locating the earth-based beacon inproximity to gateway 20, any signal loss along the propagation path fromthe earth-based beacon to satellite 10 could be used to approximate thecorrelating signal loss between satellite 10 and gateway 20. However, inalternative embodiments, one or more earth-based beacons may be locatedoutside gateway region 50.

FIG. 12 illustrates an example method 300 for use in controllingtransmitter power level on board satellite 10. At step 302, satellite 10receives a beacon signal having an amplitude (R). At step 304, theamplitude of the received beacon signal (R) is compared to a targetamplitude (T). At step 306, if the amplitude of the received beaconsignal (R) minus target amplitude (T) is greater than zero, then at step308 the gain for the signal transmitter is decreased. If at step 310,the amplitude of received beacon signal (R) minus target amplitude (T)is less than zero, then the gain for the transmitter is increased. Asshown in FIG. 12, according to certain embodiments, if the amplitude ofreceived beacon signal (R) is equal to target amplitude (T), then nochange is made to the transmitter gain. Through the use of method 300,the transmitter power level for satellite 10 may be controlled bycomparing the amplitude of a received beacon signal to a targetamplitude.

Distortion Based Power Control

In some satellite transmitters, particularly satellite transmitters usedto amplify multiple simultaneous signals distributed across thebandwidth of interest, the power levels at which the transmitterprovides acceptable performance may be half or less than half of thetransmitter's maximum power. One way to control the power level of asatellite transmitter is to perform an automatic level control (ALC)function for the signal prior to the input to the transmitter, such thatfluctuations in the input signal level are effectively negated and thetransmitter is maintained at a selected operating point relative to thetransmitter's maximum power.

On a spot-beam satellite, the number of upstream signals, the powerlevels of those signals, and therefore the total signal power at theinput to the satellite-to-gateway transmitter on the satellite may bedetermined by end-user loading. During off-peak periods, the number ofsignals at the input to the satellite transmitter may be nearly zero;while during peak periods, the number of signals at the input to thesatellite transmitter may be hundreds or thousands. The use of ALCtechniques may be insufficient when the variation in the number ofsignals and signal power at the transmitter input is large. For example,even under a fixed gain approach, the satellite amplifier power levelmay vary considerably as a function of the number of signals present.

In certain embodiments, a satellite transmitter may be maintained at aconstant or substantially constant distortion level. In particularembodiments, constant distortion level may be achieved by injecting areference signal into the transmitter input and monitoring the resultingdistortion associated with that reference signal. In these embodiments,total input power to the transmitter may be adjusted up or down tomaintain the distortion at a constant or substantially constant level.In certain embodiments, a reference signal may be injected into thetransmitter input, at the edge of the band or in a particular bandreserved for such purposes. For example, the reference signal may beselected to be in a range intended to cause little or no interferencewith the satellite-to-gateway signals. In certain embodiments, the useof distortion based power control may allow the satellite transmitter tooperate efficiently at its maximum allowable power level (relative toacceptable distortion of the satellite-to-gateway signals) across a verywide range of variation in number and power levels of input signals.

FIG. 13 illustrates example components that may be used to controlsignal power based on distortion. FIG. 13 is intended to illustrate onlythose components which may be included in payload 80 to control signalpower based on distortion. In various embodiments, the componentsillustrated in FIG. 13 may be used together with some or all of thecomponents illustrated in FIG. 4, 5, or 6A through 6B. As shown in FIG.13, test signal source 270 generates test signal 314 that is coupled toan input signal through directional coupler 272. The test signal 314,together with the input signal, is directed through controller 280 andto transmitter 282. After passing through transmitter 282, whichamplifies the input signal and test signal 314, a portion of the outputsignal (identified as distorted signal 316) is extracted usingdirectional coupler 272 and passed to filter 274. Filtered signal 318leaves filter 274 and is used as an input to controller 280. Controller280 operates to adjust the gain for transmitter 282.

FIG. 14 illustrates an example method 320 for distortion based controlof signal power. At step 322, a test signal is generated. At step 324,the test signal is coupled to a communications signal. At step 326, thecommunications signal and the test signal are amplified at anestablished gain level (G). At step 328, the amplified signals arefiltered to isolate distortion associated with the test signal. At step330, the amplitude of the isolated distortion (D) is compared to atarget distortion level (T). If, at step 332, the isolated distortion(D) minus the target distortion level (T) is greater than zero, then atstep 334, the gain is decreased. If at step 336, the isolated distortion(D) minus the target distortion level (T) is less than zero, then atstep 338, the gain is increased. Through the use of example method 320,the signal power transmitted by satellite 10 may be controlled based ondistortion levels.

FIGS. 15A through 15C illustrate example signals associated withdistortion based control of signal power. According to a particularembodiment, as shown in FIG. 15A, two narrowband tones of approximatelyequal power may be injected (along with the other transmitter inputsignals) into a satellite transmitter. A small sample of the transmitteroutput signal may be collected and the relative power level of theintermodulation product between these two tones may be monitored. Thepower level of the intermodulation product is a measure of thedistortion being caused by the satellite transmitter. If the relativepower level of the intermodulation product is less than the specifiedtarget, the gain prior to the transmitter is increased such that theinput signal level increases causing the output power of the transmitterto increase. Similarly, if the relative power level of theintermodulation product is greater than the specified target, the gainprior to the transmitter is decreased such that the input signal leveldecreases causing the output power of the transmitter to decrease. Thisprocess is designed to maintain the power level of the intermodulationproduct at or near the specified target, ensuring that the transmitteroperates at the highest possible power level that does not cause anunacceptable level of distortion.

Variations on this approach may include (1) monitoring the distortion ofthe actual transmitted signals rather than injecting a test signal; and(2) creating a narrowband notch in the bandwidth of the signal at theinput to the transmitter, either in the transmitted bandwidth or justoutside the transmitted bandwidth, and measuring transmitter distortionby monitoring to what extent the notch is filled by the transmitter.

Although the present invention has been described with severalembodiments, a plenitude of changes, variations, alterations,transformations, and modifications may be suggested to one skilled inthe art, and it is intended that the present invention encompass suchchanges, variations, alterations, transformations, and modifications asfall within the scope of the appended claims.

What is claimed is:
 1. A method of providing a redundant communicationpath for communication signals that are transmitted between a satelliteand a plurality of active gateways comprising: receiving, at a pluralityof active transceivers on said satellite, uplink communication signalsfrom a plurality of user terminals to generate a plurality of inputchannel signals; multiplexing said received uplink communication signalsto a plurality of signal channels, each signal channel comprising achannel amplifier, wherein the plurality of signal channels comprises atleast one redundant signal channel; multiplexing said signal channels togenerate said communication signals for transmission to said pluralityof gateways; transmitting said communication signals between saidplurality of active transceivers on said satellite and said plurality ofoperational gateways; detecting a change in performance of transmissionof said communication signals between said satellite and one operationalgateway of said plurality of operational gateways; directing saidcommunication signals of said one operational gateway to an additionaltransceiver in said satellite in response to detecting said change inperformance of said transmission of said communication signals of saidone active operational gateway; transmitting said communication signalsof said one operational gateway between said additional transceiver anda utility gateway.
 2. The method of claim 1 wherein said change inperformance of said communication signals between said satellite andsaid one operational gateway is due to at least a partial failure ofsaid one operational gateway.
 3. The method of claim 1 wherein saidchange in performance of said communication signals between saidsatellite and said one operational gateway is due to weatherinterference of said communication signals that are transmitted betweensaid satellite and said one operational gateway.
 4. The method of claim1, further comprising: coupling said communication signals fortransmission to said one operational gateway to an additionaltransceiver that communicates with a second utility gateway, wherein thesecond utility gateway monitors communication traffic of saidcommunication signals transmitted to said operational gateway to monitora signal strength of said communication signals transmitted to said oneoperational gateway.
 5. A satellite communication system that provides aredundant communication path for communication signals that aretransmitted between a satellite and a plurality of ground stationscomprising: a plurality of operational gateways located at saidplurality of ground stations that transmit and receive saidcommunication signals; a plurality of transceivers on said satellitethat transmit said communication signals to said plurality ofoperational gateways and receive said communication signals from saidoperational gateways, the plurality of transceivers comprising: aplurality of receivers that receive uplink communication signals from aplurality of user terminals; a plurality of input multiplexers coupledwith said plurality of receivers that generate a plurality of inputchannel signals from said received uplink communication signals; a firstplurality of channel switches coupled with the input multiplexer and aplurality of signal channels, each signal channel comprising a channelamplifier, wherein the plurality of signal channels comprises at leastone redundant signal channel; a second plurality of channel switchescoupled with the plurality of signal channels that switch each signalchannel to each of a plurality of output channel signals; and aplurality of output multiplexers coupled with the second plurality ofchannel switches that generate said communication signals fortransmission to said plurality of operational gateways; and at least oneselector on said satellite that directs at least a portion of saidcommunication signals between one operational gateway of said pluralityof operational gateways and one transceiver of said plurality oftransceivers to an additional transceiver that communicates with autility gateway in response to detection of a change in signal strengthof said communication signals transmitted between said one operationalgateway and said one transceiver, to provide said redundantcommunication path for said communication signals transmitted betweensaid one operational gateway and said one transceiver.
 6. The satellitecommunication system of claim 5 wherein said selector is operative inresponse to commands from a ground station.
 7. The satellitecommunication system of claim 5 wherein said selector directs at least aportion of said communication signals between said one operationalgateway and said additional transceiver in response to detection of saidchange in signal strength resulting from a propagation loss due toweather.
 8. The satellite communication system of claim 5 wherein saidselector directs at least a portion of said communication signalsbetween said one operational gateway and said additional transceiver inresponse to detection of said change in signal strength resulting fromat least a partial failure of said one operational gateway.
 9. Thesatellite communication system of claim 5, further comprising: a signalcoupler that couples said communication signals for transmission to saidone operational gateway to an additional transceiver that communicateswith a second utility gateway, wherein the second utility gatewaymonitors communication traffic of said communication signals transmittedto said operational gateway to monitor a signal strength of saidcommunication signals transmitted to said one operational gateway.